# 'Rate' in the rate law

I am slightly confused about what the rate is that is given by the rate law. Is it the rate of reaction (I.e. the rate of loss of reactant or formation of product divided by its stoichiometric coefficient?)

I suppose it would not make a difference to the rate equation itself if we simply used the rate of loss of reactant or formation of product without the factor of the stoichiometric coefficient, however then our rate constant would be multiplied by this factor. In that case we would have to specify what rate we are referring to when we are giving the rate constant.

My confusion stems from the fact that I have never seen it written that the rate constant is specifically determined for a given reaction, but I suppose it does not matter because rate laws are given as

$\frac {d [A]}{dt}='law'$

As opposed to just

$r='law'$

So when we actually write scientific papers we automatically specify in the expression of the equation what rate we are referring to. And then if we wished to transfer this rate law to give the change in concentration of another reactant or product we would use the stoichiometric relations and it would indeed change the value of the rate constant for a given rate law...

I apologise if I have not expressed myself clearly. I am starting out learning about this topic so have just looked at rate laws in theory and have not come across them in papers or seen how they are given in practice. Would appreciate if someone could verify if my thinking is correct or not?

• If you take a look in the IUPAC Gold Book, the rate of reaction is defined unambiguously. The idea is that you have to divide through by the stoichiometric coefficient. I also wrote a bit about it some time ago chemistry.stackexchange.com/a/38168/16683 – orthocresol Mar 11 '17 at 12:59